1. Field
One or more embodiments relate to a medium feeder such as a paper feeder, and particularly, to a stable auto document feeder (ADF) capable of normally and stably picking up various kinds of print medium such as various kinds of sheets of paper, and a scanner including the ADF and a method of controlling auto document feeding.
2. Description of the Related Art
Auto document feeders (ADFs) are used to control picking up and feeding of sheets of paper and scanning of images of the sheets of paper. FIG. 1 is a view illustrating a paper feed operation of an ADF. Referring to FIG. 1, after a sheet of paper is picked up and carried a predetermined distance, a sensor 120 placed along an ADF path generates a turn-on signal, and the next operation is performed.
First, as shown in FIG. 1, a pickup mechanism is moved to a position 100 adjacent to a paper side for starting a paper pickup operation. After the paper pickup operation, the pickup mechanism is moved back to a position 110 as shown in FIG. 1. In addition, if the paper pickup operation is repeated, the pickup mechanism is moved away from the paper side.
If the sensor 120 does not generate a turn-on signal, the paper pickup operation is repeated, and if the number of repetition times is equal to or greater than a maximum number of times, an error message is displayed.
FIG. 1 also shows feed rollers 130, scan rollers 140, exit rollers 150, sheets 160, and sheets 170.
FIG. 2 is a block diagram illustrating a paper control unit of an ADF. The paper control unit includes a feed control unit 200 and a scan control unit 250. Referring to FIG. 2, when paper feeding is normally performed, the feed control unit 200 controls the paper feeding, and then the scan control unit 250 controls image scanning. Before the feed control unit 200 controls paper feeding, the speed of a motor may be increased or decreased, and a current supplied to the motor may be controlled.
If paper feeding is not normally performed, a paper feed operation of the feed control unit 200 may be repeated to normally feed a sheet of paper. If a sheet of paper is not normally fed although the paper feed operation is repeated, an error message is displayed.
FIG. 3 is a graph illustrating how the speed of a paper feed motor is controlled. FIG. 4 is a graph illustrating how a current to the paper feed motor is controlled. Referring to FIGS. 3 and 4, if a sheet of paper is not normally picked up, a feed control unit repeats a paper feed operation while keeping the speed of the motor at a constant level and supplying a constant current to the motor.
For example, when a user intends to read images of various kinds of sheets of paper (documents) by scanning the sheets of paper using a paper feeder of an ADF, paper feeding may not be normally performed due to the variety of types of sheets of paper. Then, the paper feeding may be repeatedly performed, and if a sheet of paper is not normally picked up although the paper feeding is performed a maximum number of times, an error message may be displayed. If a sheet of paper is not normally picked up although the paper is performed a maximum number of times, sheets of paper (documents) may not be conveniently scanned and read.